Effect of different cations on the ferroelectric properties of modified strontium barium niobate ceramics

Abstract

Strontium barium niobate (SBN) is a ferroelectric solid solution with tetragonal tungsten bronze structure [1, 2]. The structure consists of a framework of oxygen octahedra sharing corners in such a way that there are three different types of interstitial sites A, B and C. The common formula is (A1)2(A2)4(C)4(B1)2(B2)8030, where positions At , A2, BI, B2 and C can be filled by different-valency cations or may be partially empty. In tungsten bronze niobates BI and B 2 are filled by Nb 5+ . As, A2 and C could be filled by alkali and alkaline-earth metal ions from which crystals and solid solutions could be prepared with a variety of cations introduced into the structure. In many of these materials diffuse phase transition has been reported. In the work of Jimenez et al. [3] on SBN ceramics a large decrease in the Curie temperature of nearly 50 °C was reported when doped with Fe, Mn, Cr and La. Hence, in this work by doping with suitable cations we have tried to enhance Tc and decrease the dielectric loss. When the interstitial vacancies are filled partially or fully with alkali elements, Tc is raised. Hence, for filling the structure Na + was introduced. With the introduction of Na +, Aposition vacancies result from the volatility of Na. It is well known that A-position vacancies aid the sintering process. Lattice vacancies may be expected to be effective promoters of sintering because sintering is basically diffusion-controlled. Also, the ionic radius of Na + is smaller than that of Sr or Ba. This difference in ionic size is enough of a defect to cause marked lattice reconstruction by diffusion. The effect of different cations Cr 6+ , Zn 2+ and y3+ on the lattice parameters and ferroelectric properties of SrBaNb20 6 ceramics are reported in this letter. Polycrystalline solid solutions of the following compositions are prepared by the conventional ceramic processing: (Sr0.6Ba0.4)0.s RyNa0.4Nb206